The following non-patent literature references are believed to reflect the state of the art:
EPIC: Ending Piracy of Integrated Circuits, J. A. Roy, F. Koushanfar, I. L. Markov., DATE '08, Proceedings of the conference on Design, Automation, and Test, in Europe, pages 1069-1074;
Designing Chips That Protect Themselves, F. Koushanfar and I. L. Markov, ACM DAC Knowledge Center, March 2010;
IC Activation and User Authentication for Security-Sensitive Systems, J. Huang and J. Lach, Hardware-Oriented Security and Trust, 2008. HOST 2008, pages 76-80;
Security Through Obscurity an Approach for Protecting Register Transfer Level Hardware IP, Chakraborty, R. S.; Bhunia, S., Hardware-Oriented Security and Trust, 2008. HOST 2008, pages 96-99;
CLIP: Circuit Level IC Protection Through Direct Injection of Process Variations, W. P. Griffin, A. Raghunathan, and K. Roy, IEEE Transactions on Very Large Scale Integration (VLSI) Systems, May 2012, Vol. 20, no. 5, pages 791-803; and
Integrated Circuits Metering for Piracy Protection and Digital Rights Management: An Overview, F. Koushanfar, GLVSVLSI, 2011.
The following patent literature references are also believed to reflect the state of the art:
US 2009/0182919 of Chang, et al.;
US 2010/0287374 of Roy, et al.;
US 2010/0122353 of Koushanfar, et al.;
US 2010/0284539 of Roy, et al.;
U.S. Pat. No. 5,530,753 to Easter, et al.;
U.S. Pat. No. 5,708,715 to Vicard;
U.S. Pat. No. 6,571,335 to O'Donnell, et al.; and
U.S. Pat. No. 7,490,245 to Waltermann, et al.